Cutting edge: human eosinophils regulate T cell subset selection through indoleamine 2,3-dioxygenase

Allergy involves eosinophilia and Th2 polarization. Indoleamine 2,3-dioxygenase (IDO)-catalyzed conversion of tryptophan to kynurenines (KYN) regulates T cell function. We show that human eosinophils constitutively express IDO. Eosinophils treated with IFN-gamma showed an 8-fold increase in IDO mRNA within 4 h; IL-3, IL-5, and GM-CSF had no effect on baseline IDO expression. IL-3 pretreatment of eosinophils reduced IFN-gamma-induced IDO mRNA expression below baseline. Conversely, GM-CSF, but not IL-5, resulted in a 2-fold increase in IFN-gamma-induced IDO. Treatment with IL-3, IL-5, GM-CSF, or IFN-gamma alone expressed IDO enzymatic activity (the presence of KYN in supernatants 48 h postculture). CD28 cross-linking resulted in measurable KYN in culture supernatants, inhibitable by a neutralizing anti-IFN-gamma. Coculture of eosinophils with an IFN-gamma-producing T cell line, but not IL-4-producing T cell clone, led to apoptosis and inhibition of CD3 or CD3/CD28-induced proliferation. Eosinophils infiltrating asthmatic lung and associated lymphoid tissue exhibited intracellular IDO immunoreactivity. Eosinophils may, therefore, maintain Th2 bias through IDO.

[Study of indoleamine 2,3-dioxygenase expression in patients of esophageal squamous cell carcinoma]

We evaluated the clinical significance of indoleamine 2,3-dioxygenase (IDO) in esophageal squamous cell carcinomas. Operative specimens obtained from 30 patients with esophageal squamous cell carcinomas were investigated by semiquantitative RT-PCR with specific primers against IDO. The correlations among IDO expression, clinicopathologic factors and prognosis were studied. The expression of IDO was observed in 100% of both of the cancer specimens and the normal mucosa specimens. The IDO expression of the cancer specimens was higher than the normal mucosa specimens. The expression of IDO did not correlate to histological classification, growth pattern, lymphatic invasion, venous invasion, or lymph nodes metastasis, but correlated to clinicopathological stage, the value of immunosuppressive acidic protein (IAP). The group with higher levels of IDO expression had a worse survival rate than the IDO expression group with lower levels. The serum IDO levels of cancer patients were higher than healthy donors measured by semiquantitative RT-PCR and HPLC. It is suggested that the expression of IDO in esophageal squamous cell carcinoma patients may play a pivotal role for immunosuppression of those patients.

Gender based response to fluoxetine hydrochloride medication in endogenous depression

OBJECTIVE

To determine the gender based response to fluoxetine HCl medication in relation to tryptophan metabolism in depressed patients.

DESIGN

A comparative, analytical study.

PLACE AND DURATION OF STUDY

Clinical Biochemistry and Psychopharmacology Research Unit, Department of Biochemistry, University of Karachi during the year 2002 to 2003.

SUBJECTS AND METHODS

Sixteen adults depressed patients who were not having any other major comorbidity were selected from the outpatients department of local psychiatric clinic for the study. They were subjected to a semi-structured interview for associated clinical characteristics and diagnosis of depression according to ICD-10 criteria. A control group of normal health male and female individuals was identified for comparison with the depressed group. All the depressed patients were treated with fluoxetine hydrochloride (Prozac 20 mg/day) for four weeks. Healthy individual's data was compared with the depressed group and evaluated for gender based response to fluoxetine HCl medication.

RESULTS

Significant decreases were found in total tryptophan concentrations (33 %, p<0.01,56%, p<0.01) in depressed male and female patients respectively, in contrast, serum cortisol levels were increased by 68% and 98% in male and female depressed patients respectively as compared to healthy controls. Significant increases (23%, p<0.05) in albumin levels were found in females only. Four weeks treatment of male and female depressed group by Fluoxetine HCL (Prozac) 20 mg/kg/day, increased serum total tryptophan concentrations significantly by 32% (p<0.05) in males and by 83% (p<0.01) in females. Serum-free tryptophan concentrations were increased by 22% (p<0.05) in males only. In contrast serum cortisol concentrations were decreased by 31% (p<0.01) and 45.35% (p<0.01) in males and females respectively.

CONCLUSION

Increases in tryptophan and decreases in cortisol concentrations were greater in females which may contribute to better response of the drug in females.

Brain virus burden and indoleamine-2,3-dioxygenase expression during lentiviral infection of rhesus monkey are concomitantly lowered by 6-chloro-2',3'-dideoxyguanosine

Increased kynurenine pathway metabolism has been implicated in the aetiology of lentiviral encephalopathy. Indoleamine-2,3-dioxygenase (IDO) initiates the increased production of kynurenine pathway metabolites like quinolinic acid (QUIN). QUIN itself is elevated in AIDS-diseased monkey and human brain parenchyma and cerebrospinal fluid at levels excitotoxic for neurons in vitro. This study investigates the cellular origin of IDO biosynthesis in the brain of rhesus monkeys infected with simian immunodeficiency virus (SIV) and explores the effects of CNS-permeant antiretroviral treatment. IDO transcript and protein were absent from the brain of non-infected and SIV-infected asymptomatic monkeys. IDO biosynthesis was induced in the brain of monkeys exhibiting AIDS. Nodule and multinucleated giant cell-forming macrophages were the main sources of IDO synthesis. Treatment with the lipophilic 6-chloro-2',3'-dideoxyguanosine suppressed IDO expression in the brain of AIDS-diseased monkeys. The effectiveness of this treatment was confirmed by the reduction of virus burden and SIV-induced perivascular infiltrates, mononuclear nodules and multinucleated giant cells. Our data demonstrate that brain IDO biosynthesis is induced in a subset of monocyte-derived cells, depends on viral burden and is susceptible to antiretroviral treatment. Thus, IDO induction is associated with reversible overt inflammatory events localized to areas of active viral replication in the SIV-infected brain.

Induction of indoleamine 2,3-dioxygenase in primary human macrophages by HIV-1

Increased kynurenine pathway metabolism has been implicated in the aetiology of the AIDS dementia complex (ADC). The rate limiting enzyme for this pathway is indoleamine 2,3-dioxygenase (IDO). We tested the efficacy of different strains of HIV-1 (HIV1-BaL, HIV1-JRFL and HIV1-631) to induce IDO in cultured human monocyte-derived macrophages (MDM). A significant increase in both IDO protein and kynurenine synthesis was observed after 48 h in MDM infected with the brain derived HIV-1 isolates, laboratory adapted (LA) HIV1-JRFL, and primary isolate HIV1-631. In contrast, almost no kynurenine production or IDO protein was evident in MDM infected with the high replicating macrophage tropic LA strain, HIV1-BaL. The induction of IDO and kynurenine synthesis by HIV1-JRFL and HIV1-631 declined to baseline levels by day-8 post-infection. Together, these results indicate that only selected strains of HIV-1 are capable of inducing IDO synthesis and subsequent oxidative tryptophan catabolism in MDM.

Elevated basal activity of tryptophan oxygenase in alcohol-preferring C57BL mice

Tryptophan oxygenase activity in alcohol-preferring C57Bl mice and control CBA and DBA/2 mice was studied under nonstressful conditions and after glucocorticoid-induced stress. Elevated basal tryptophan oxygenase activity in C57Bl mice is probably responsible for reduced brain content of tryptophan and serotonin associated with alcohol preference.

Interferon-gamma-induced activation of indoleamine 2,3-dioxygenase in cord blood monocyte-derived macrophages inhibits the growth of group B streptococci

Neonatal sepsis is most often caused by group B streptococci (GBS) and is a major cause of death in the neonatal period. The response of the immune system in the newborn child has received much attention and is thought to be deficient in a number of ways. The effector response of neonatal monocyte-derived macrophages (MDM) was investigated. Interferon-gamma induced the activation of indoleamine 2,3-dioxygenase in MDM and inhibited the growth of GBS. Both effects were enhanced by the addition of tumor necrosis factor-alpha to the culture conditions. The coincident supplementation of L-tryptophan with the bacteria abrogated the bacterial growth inhibition, thus confirming the causative role of L-tryptophan depletion. Control of the extracellular as well as intracellular L-tryptophan levels may thus be one of the effector mechanisms with which the immune system defends the host against GBS dissemination and disease.

Tryptophan metabolism in male Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats

Parameters of tryptophan (Trp) and related metabolism were compared in male Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats. Liver Trp pyrrolase activity was 38-58% higher in sP than in sNP rats, and this was associated with a greater expression of the enzyme mRNA as measured by multiprobe oligonucleotide solution hybridization. Moderately (about 10-19%), but significantly, lower concentrations of free serum, total serum, and brain Trp were also observed in sP compared with sNP rats. Concentrations of whole brain 5-hydroxytryptamine (5-HT) and its major metabolite 5-hydroxyindol-3-yl-acetic acid (5-HIAA) were, however, 14-21% higher in sP rats. Serum corticosterone concentration was 18% higher in sP rats. We conclude that alcohol preference in Sardinian rats is associated with increased liver Trp pyrrolase activity and mRNA expression leading to a decrease in Trp availability to the brain. Although a simple serotonin deficiency could not be demonstrated in the whole brain, the possibility could not be ruled out that a deficiency may be present in discrete areas of the brain of the sP rat.

Decreased serum tryptophan in patients with cancer cachexia correlates with increased serum neopterin

We investigated serum tryptophan (Trp), neopterin (NPT) and immunosuppressive acidic protein (IAP), one of tumor-associated tumor marker, concentrations in 28 patients with gastrointestinal tumors representing cancer cachexia and 10 healthy controls. NPT comes from activated macrophages presumably activated by tumor-sensitized T cells via gamma-interferon (IFN-gamma) excitation of the macrophages. We found that the NPT level was significantly higher than the control value. The negative correlation of NPT and Trp concentrations indicates activity of indoleamine 2,3-dioxygenase (IDO), a Trp degradating enzyme, in cancer-burden patients. The activity of IDO can be induced by cytokines such as IFN-gamma, and therefore low Trp levels may result from endogenous IFN-gamma production due to immune activation against tumors. We also found a positive correlation between NPT and IAP levels, suggesting that host immune activation against tumors played a role in the immunosuppression of cancer-burden states, followed by cancer-cachexia.

Alteration of mice L-tryptophan metabolism by the organophosphorous acid triester diazinon

Diazinon [O,O-diethyl O-(2-isopropyl-6-methyl-4- pyrimidinyl)phosphorothioate] altered the formation of several L-tryptophan metabolites associated with the L-kynurenine pathway in mice. Liver kynurenine formamidase was inhibited almost completely by diazinon (10 mg/kg). The enzyme inhibition resulted in reduced L-kynurenine biosynthesis in livers with a concomitant accumulation of N-formyl-L-kynurenine. In contrast to the liver, plasma L-kynurenine increased up to 5-fold in diazinon-treated mice. Consequently, the urinary excretion of xanthurenic acid and kynurenic acid was raised 5- to 15-fold. The revelation of this novel mechanism of diazinon action is an important piece of information needed for a better understanding of the noncholinergic toxicity of organophosphorous acid triesters and methylcarbamates.

Increase in tryptophan oxygenase activity in alcoholic patients

This study was conducted in order to assess whether chronic excessive alcohol consumption affects the activity of the liver enzyme tryptophan oxygenase which is rate limiting along the most important pathway of tryptophan catabolism. Five alcoholics were studied twice, once shortly after admission to an inpatient unit and the second time 1 month later. On each study day patients were given a tryptophan load of 50 mg/kg. Kynurenine in the urines (which reflects tryptophan oxygenase activity) was measured for a period of 6 hr following the load and showed a significantly enhanced activity of the enzyme shortly after cessation of drinking. This increased activity could explain the lowered tryptophan levels we have previously reported in alcoholics. The increase in enzyme activity may have been mediated by a rise in glucocorticoid hormones. In all instances, plasma cortisol measured hourly for 6 hr after the start of the experiment, was higher shortly after cessation of drinking than 1 month later.

Multihormonal regulation of transcription of the tryptophan 2,3-dioxygenase gene in primary cultures of adult rat hepatocytes with special reference to the presence of a transcriptional protein mediating the action of glucocorticoids

For study of hormonal regulation of gene expression of tryptophan 2,3-dioxygenase (EC 1. 13. 11. 11, TO), a DNA clone containing a sequence complementary to TO mRNA was prepared with TO mRNA from rat liver enriched 62-fold by immunoadsorption. Primary cultures of adult rat hepatocytes were treated with dexamethasone, and the amount of TO mRNA was measured by RNA dot-blot hybridization with this TO cDNA. Dexamethasone induced this TO mRNA 7-fold, while their treatments with dexamethasone plus glucagon induced the TO mRNA 18-fold. This induction of TO mRNA by dexamethasone plus glucagon was inhibited by insulin or epinephrine. Studies on transcription in isolated nuclei showed that these hormonal changes in the level of TO mRNA were caused by changes in the rate of transcription of the TO gene. Thus, expression of TO in the liver is regulated multihormonally at the transcriptional step. There was a long lag period before stimulation of transcription of the TO gene by dexamethasone in hepatocytes cultured for 20 h: the maximal rate was attained after 6-8 h. The lag time depended on the culture time without dexamethasone and was shorter after shorter culture of the cells. This finding suggested that a transcriptional factor that was lost during culture mediated the action of glucocorticoids. Consistent with this idea, cycloheximide or puromycin almost completely blocked enhanced transcription of the TO gene by dexamethasone after a 20-h culture, but not after a 2-h culture. These findings indicate that a short-lived transcriptional protein, which is also regulated by glucocorticoids, mediates their effect on expression of the TO gene.

Stimulation of liver tryptophan pyrrolase during heat exposure

Exposure of rats to heat (39 +/- 1 degree C) stimulated liver tryptophan pyrrolase 2-fold between 3 and 48 h. Plasma corticosterone increased 2-fold after 1 h of heat exposure and decreased to a low value of 50% by 16 h. The effect of heat exposure on the enzyme was obtained in adrenalectomized animals. Stimulation by cortisol and tryptophan of the enzyme was also obtained in heat exposure, and the effects seemed to be additive. The concentration of tryptophan in the liver remained unchanged, and that in the plasma decreased to about 50% at 8 h exposure to heat and reverted to normal by 46 h. Simultaneous administration of noradrenaline to heat-exposed rats had no effect, whereas that of thyroxine partly prevented the stimulation of the enzyme activity. Hypothyroid conditions obtained by thyroidectomy or treatment with propylthiouracil significantly stimulated the enzyme activity. Cycloheximide treatment of heat-exposed rats did not prevent the stimulation of the enzyme activity. The results indicate that the effect of heat exposure on liver tryptophan pyrrolase is obtained, due to the accompanying hypothyroid condition, by increasing the activity of the existing protein by a mechanism possibly different from those known at present.

Abnormal tryptophan pyrrolase and amino acids related to melanogenesis in vitiligo

A comparison of the serum tyrosine, DOPA, tryptophan, tyrosinase and tryptophan pyrrolase levels of vitiliginous patients with those of normal subjects show abnormalities in all these parameters. As the clinical diagnosis of vitiligo may be made without difficulty, these parameters appear to be of little diagnostic value in vitiligo. But they may be considered as additional biochemical parameters in vitiligo.

Selective ion monitoring of tryptophan, N-acetyltryptophan and kynurenine in human serum. Application to the in vivo measurement of tryptophan pyrrolase activity

A specific method is described for the determination of deuterated and non-deuterated N-acetyltryptophan, tryptophan and kynurenine in human serum and urine using gas chromatography-mass fragmentography. N-Acetyltryptophan was analysed as the N-trimethylsilyl methyl ester derivative; tryptophan and kynurenine were converted into their N-pentafluoropropionyl methyl esters. N-Acetyl-DL-tryptophan-d11, tryptophan-d8 and kynurenine-d2 were used as internal standards. The coefficients of variation were found to be about 8% (n = 9) for tryptophan and N-acetyltryptophan and about 2.4% (n = 9) for kynurenine. Using this method, an in vivo determination of the tryptophan pyrrolase activity [L-tryptophan oxygen 2,3-oxidoreductase (decyclizing), E.C. 1.13.11.11] is possible by loading the subjects with deuterated L-tryptophan-d5 and subsequently measuring the deuterated L-kynurenine-d4 formed and the residual L-tryptophan-d5.